Wow - so many people seem to disclose!
I tend to disclose my depression and agoraphobia these days, because they're both pretty widely understood here, and people don't seem to wonder how to react appropriately. I've always been concerned that my ptsd wouldn't be well understood (people won't know to attribute my strange behaviour to it, even if they knew).
But more than that, I worry that it begs as many questions as it answers for people...what was the trauma? Is she going to flip out? am I going to say something that upsets her? If I was already anxious in a particular setting, I might disclose the anxiety (people kinda get it), but disclosing my ptsd would make me even more anxious. Just me.
And while I always think it's amazingly courageous when people are able to put it out there, and that's absolutely necessary to reduce stigma, there is no onus on any one individual to disclose their situation for the greater good. I think that should be a consideration (& inspiration) to disclose, but not the key factor in your decision.
With my study, I disclose confidentially to my lecturer to explain my sometimes odd behaviour, need to suddenly leave class etc, and that helps a lot. Telling just the president might be an option, as a starting point. Eg "I'm keen to participate but sometimes I might need to ... because of my ptsd." Just an idea.